1. Field of the Invention
The present invention relates to a photo detective unit and an electric apparatus using the same. More particularly, the present invention relates to a photo detective unit used for data transmission with light and an electric apparatus such as a remote controller using the photo detective unit.
2. Description of the Background Art
In the case of electric apparatuses including video apparatuses such as televisions and VTRs (Video Tape Recorders) and audio apparatuses such as stereos, which are provided with remote controllers, operation of each electric apparatus can be controlled even from a distance by operation of the remote controller. Data transmission of the remote controller is generally carried out with radiowaves or infrared rays. For domestic use, a remote controller with infrared rays having a shorter signal reachable distance but having less interference and also being cheaper is often used.
FIG. 5 is a block diagram showing a photo detective unit provided within a conventional remote controller. In
FIG. 5, photo detective unit 4 includes a photodiode 41 and a signal processing IC (Integrated Circuit) 42, both of which are accommodated in a metal case 45. Photodiode 41 is an element through which current flows according to a light quantity of infrared rays L, and this current is applied through an interconnection 44 to signal processing IC 42. Signal processing IC 42 converts current flowing in photodiode 41 into voltage, carries out waveform shaping for removing an infrared ray carrier signal contained in the voltage signal, and demodulates a digital data signal transmitted from the remote controller for transmission to a control circuit of each electric apparatus.
However, a photodiode for use in such a photo detective unit generally has such a property that photocurrent may change only by about several .mu.A per 100 lux light, and therefore, the output impedance thereof will be increased. Accordingly, since the impedance of interconnection 44 for connecting photodiode 41 with signal processing IC 42 in photo detective unit 4 shown in FIG. 5 is increased and interconnection 44 is long with a length of at least several mm, an error signal resulting from noise from the outside of photo detective unit 4 is likely to be generated in interconnection 44, and a wrong data signal is transmitted to each electric apparatus, so that the electric apparatus might carry out operation different from that designated by the remote controller.
In order to prevent this, the whole photo detective unit is generally shielded with metal case 45 from noise, but in this case, the size of metal case 45 will be increased. If photo detective unit 4 is large in size, reduction in size of each electric apparatus provided with the photo detective unit is prevented, so that an external shape (design) of each electric apparatus may be restrained. Furthermore, purchase of the metal case and maintenance cost thereof are additionally required.
On the other hand, photo detective unit 4 could be formed with a one-chip semiconductor device, and in that case, only a short interconnection between photodiode 41 and signal processing IC 42 such as that having a length of several tens or several hundreds of .mu.m is required, and therefore, the photo detective unit is less likely to be subjected to external noise, whereby shielding of the whole photo detective unit with metal case 45 will not be necessary. However, in order to provide a semiconductor device having as small chip size as possible at low cost, a signal processing circuit and a photodiode are simultaneously formed with manufacturing conditions (processes) for formation of the signal processing circuit, resulting in difficulty in sufficient increase in the infrared ray detecting capability (photosensitivity) of the photodiode.